This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. An elevated plasma level of low density lipoprotein (LDL)-cholesterol is a major risk factor for atherosclerotic coronary artery disease (Gotto and Pownall, 1999). LDL comprises a neutral lipid core of cholesteryl esters (CEs) and triglycerides, surrounded by a surface monolayer of phospholipids, free cholesterol, and apolipopro-tein B-100 (apoB-100), which contains the ligand for the LDL-receptor (LDLR) that initiates LDL endocytosis, a key step in cholesterol metabolism. The molecular basis of LDL endocytosis would be better understood if we could determine the structure of the LDL/LDLR complex. We are interested in determining the cryo-EM structure of the LDL and LDLR complex.